1. Field of the Invention
The present invention relates to a hybrid induction motor, and particularly to a driving circuit for improving starting of a hybrid induction motor and its method, which is capable of obtaining a satisfactory starting characteristic by increasing output under a low-voltage state in starting, and capable of performing effective operation by decreasing output under a normal operation state after the starting is completed.
2. Description of the Background Art
In general, in a hybrid induction motor, since a normal torque and a reversed-phased torque are harmonized, an actual starting torque becomes ‘0’. Therefore, in starting, the hybrid induction motor is started as a two-phase induction motor by using a auxiliary-coil, and when the starting is completed, the hybrid induction motor is operated as a single-phase motor by isolating the auxiliary-coil from a main coil.
FIG. 1 illustrates a circuit schematically showing a starting unit of a general single-phase induction motor.
As shown in FIG. 1, in a driving circuit of a general hybrid induction motor, a auxiliary-coil 2 is connected in parallel to a main coil 1 which is connected in series to commercial power, and a capacitor (Cr) 3 for operation for generating a rotating magnetic field is added between the main coil and the auxiliary-coil.
In the starting unit of a hybrid induction motor constructed as above, in an initial stage of starting, the power of the capacitor for operation maintains an ON-state and thus a current flows to the auxiliary-coil, whereby the hybrid induction motor is operated as a two-phase induction motor to generate a starting torque. At this time, when the induction motor is operated at a normal speed, the power of the capacitor for operation becomes OFF-state, thereby cutting off a current that is applied to the auxiliary-coil 2. Thereafter, a current is applied to the main coil 1, thereby rotating a single-phase induction motor.
However, in the abovementioned hybrid induction motor is disadvantageous in that a minimum voltage needed for starting the motor is increased, thereby degrading reliability. In addition, if the hybrid induction motor is designed so as to start under a low voltage state, a large rotating torque and a large consumption power are needed in normal operation, thereby degrading operation efficiency.